The present invention concerns a method for producing layers that are generated from mixtures that contain a liquid crystal material and are homogenous and isotropic at suitable temperatures and, after appropriate cooling, have a coherent polymer structure with isolated liquid crystal compartments. These layers are suitable for use in electro-optical displays.
Electro-optical display cells are comprised in general of two panes or plates that are spaced apart from one another by a few μm of which at least one plate is light-transmissive. The plates are pretreated on their inner side in a suitable way, for example, coated with ITO (indium tin oxide), in order to provide electrical conductivity. Between the plates there is a liquid crystal layer. In order to secure the plates so as to be equidistantly spaced apart from one another, spacers are usually employed that, for example, are comprised of balls produced from mineral or organic material or rods or walls produced by UV light. However, the non-uniform distribution, the yielding action when exposed to external pressure, and the unsatisfactory mechanical stability have disadvantageous effects on the display function.
Known in the art are polymer-dispersed liquid crystals (PDLC) that are comprised of micro-heterogeneous liquid crystal polymer composites and are used as electro-optical light switches. Polymer components contained therein are in general incoherent. In order to achieve the desired scattering conditions, the dimensions of the LC regions must be matched accordingly, for example, for visible light must have a diameter of approximately 0.3 to 3 μm. Such polymer-dispersed liquid crystals are disclosed, for example, in WO 87/01822, EP 540353 B1, and WO 2005/072304. Inasmuch as they fulfill further required conditions, they can be switched with the aid of an electric field between a light-scattering and a transparent state. Light scattering, in the context of the present invention, is an effect that should be prevented as much as possible.
In U.S. 2004/0119911 A1 a liquid crystal display with thermal-optical properties is disclosed. The size of the liquid crystal droplets is not indicated therein.
It is an object of the present invention to provide liquid crystal layers for display cells whose intrinsic properties lead to an improved mechanical stability of the display cells. Moreover, it is an object of the present invention to provide liquid crystal layers whose optical properties can be influenced region-selectively without having to fear a later intermixing of the selectively influenced regions with other regions. In a preferred embodiment of the invention, the object of providing display cells that, despite high mechanical stability, are bendable without causing destruction of the region-selective controllability is to be solved furthermore.